This invention relates to a hearing aid device and more particularly to a hearing aid which incorporated improved clipping circuitry to provide improved performance.
Hearing aid users with sensorineural hearing losses commonly complain of an inadequate listening level at which they are comfortable. Further complaints of such users involve a loudness discomfort attendant with an inability of the user to understand speech in noisy situations. The inadequate comfortable listening level is due partly to the frequency response of the hearing aid as effecting the user's ear and the general inability of the hearing aid circuit to provide adaptive filtering as a function of the listening level of the user.
Generally speaking, the real ear frequency response in combination with the hearing aid frequency response are attendant with the following limitations:
Basically, low frequcny energy having large peak amplitudes serves to control the gain level at which the user is comfortable. For example, a hearing aid user will adjust his volume control to a comfortable listening level by making reference to low frequency peaks which are the more intense stimuli. In certain hearing aids which employ input compression circuits, the low frequency peaks serve to reduce the compressor gain which deprives the user of a comfortable listening gain setting.
In other devices employing output compression circuits, the low frequency peaks result in large compression ratios. The operation of the low energy peaks in such aids result in severe intensity distortion of the signal. Hence, the user is unable to resolve differences in intensity and his hearing acuity is degraded.
A technique of reducing low frequency energy peaks is commonly referred to as peak clipping. Such peak clipping circuits are employed in conventional hearing aids. In any event, the operation of a peak clipper serves to generate high levels of harmonic distortion. Particularly, such clippers may operate to generate high levels of third harmonic distortion. This distortion produced degrades the speech information by masking the weaker speech elements and hence, the user is deprived of meaningful cues.
It is therefore an object of the present invention to provide a hearing aid which substantially reduces low frequency peak energy, while maintaining a sufficient gain and response to enable reliable hearing acuity.